During the process of converting pressure-sensitive bulk products such as rolls of a laminate of a face stock or backing, a pressure-sensitive adhesive layer, and a release liner into end products, many cutting operations are performed. These include slitting, sheeting, guillotining including hole punching and perforating, and die cutting on rotary and flat-bed machines.
Die cutting for label manufacture is the most complex. There, a laminate of a face stock or backing, pressure-sensitive adhesive layer and a release liner is passed through apparatus which converts the laminate to yield commercially useful labels from label stock. The processes involved in converting operations include printing, die cutting and matrix stripping to leave labels on a release liner, butt cutting of labels to the release liner, marginal hole punching, perforating, fan folding, guillotining and the like.
Die and butt cutting involve cutting of the laminate to the face of the release liner. Other procedures involve cutting clean through the label laminate and include hole punching, perforating and guillotining.
The cost of converting a laminate into a finished product is a function of the speed at which the various processing operations occur. While the nature of all layers of the laminate can impact cost of convertability, the adhesive layer has been the greatest limiting factor in ease and cost of convertability. This is in consequence of its viscoelastic nature which hampers precise and clean penetration of a die in die cutting operations and promotes adherence of the adhesive to cutting blades and the like in converting operations.
For slitting and sheeting, the cutting blade, because of adhesive adherence, becomes tacky and forms so called "gum balls." The gum balls transfer to the surface of paper and produce product defects. Quite often, the operators have to stop the cutting operation and clean the blade. Placing a lubricant such as mineral oil on the surface of the blade can help the cutting process.
For die cutting, poor cutting causes matrix breaks when waste matrix is peeled off. In order to avoid the matrix breaks, the press operators are forced to lower the converting speed.
For guillotining where stacks of sheets are cut at the same time, the cutting edge of the paper tends to become tacky. As a result the separation of each sheet becomes difficult and subsequent printing process may be jammed.
In order to improve the converting process, minimization of adhesive adherence to cutting blades is most important. PG,4
U.S. Pat. Nos. 4,151,319 to Sackoff et. al and 4,346,189 to Laurent claim addition of silicone oil and gums to adhesive compositions. These additives improve cutting performance, but at a sacrifice in adhesion.
While not directly related to cutting performance, U.S. Pat. No. 4,693,935 to Mazurek discloses polysiloxane-grafted adhesive copolymers. The adhesive compositions claimed are repositionable with adhesive-bonding building upon dwell for an extended time.
U.S. Pat. No. 4,548,845 to Parsons et. al teaches the addition of a polyoxyalkylene polyol such as polyethylene glycol to tackified water-insoluble adhesives to reduce the adhesive build-up on a knife blade during guillotine cutting. This has resulted in phase separation and incompatibility in some adhesive systems.